Mass storage systems are commercially available for storing large volumes of data on various types of storage media. For example, mass storage systems are widely available for storing data on magnetic tape cartridges. These mass storage systems are relatively inexpensive, rugged, and highly reliable for managing large quantities of data. Hard disk drive storage, while faster and often more reliable than tape storage, has typically been more expensive.
However, the cost of hard disk drive storage has dropped at the same time storage capacity has increased. Accordingly, hard disk drive storage has become a viable alternative to magnetic tape cartridges. For example, server computers are often configured with multiple hard disk drives, referred to as redundant arrays of independent disks (RAID) storage. RAID storage includes two or more hard disk drives with mirror copies of the data and provide fault tolerance and enhanced performance.
Electrical cables are typically used to connect the hard disk drives to the processor to support high data transfer rates. However, the high data transfer rates over electrical cables (currently around 1 GHz) results in electromagnetic interference (EMI) that may need to be shielded. In addition, the hard disk drives typically must be positioned in close proximity to the processor (e.g., within 18 inches for advanced technology attachment ATA hard disk drives) for data transfer, and the number of devices on the bus may be limited.